The objective of the studies, in this proposal is to determine whether changes in cyclic nucleotide levels within mammalian oocytes or their microenvironments are involved in stimulating the resumption of the first meiotic division. This will be accomplished in three series of experiments. In the first, we will measure changes in cyclic AMP and cyclic GMP levels in denuded mouse oocytes and cumulus enclosed rabbit oocytes maturing spontaneously in culture. The same information will be obtained for the above oocytes and their cululi oophori as they mature in cultured intact follicles in response to LH stimulation. In the second series, we will measure cyclic nucleotide levels in human follicular fluid obtained by follicular aspiration during laparoscopy at variuos times after the onset of the mid-cycle LH surge. The interpretation of these data and those in the above experiments should contribute significantly toward clarifying the present confusion (see literature review) concerning the role of cyclic nucleotides in mammalian oocyte maturation. In the third series of experiments, substances known to affect the spontaneous maturation of oocytes (denuded or cumulus-enclosed) and the expansion (mucification) of cumulus cells in vitro will be examined for their ability to change cyclic nucleotide levels in these structures. The effects of LH, theophylline, cholera enterotoxin, steroids, prostaglandin E1 and substances affecting CA++ movement will be tested. The interpretation of these data are expected to define changes in the relationships between cumulus and oocytes that are important for the resumption of meiosis. In depth understanding of this necessary prerequisite for fertilization may provide valuable information which can subsequently be used for prevention of ovulation and fertility control.